Distilland by-pass means multi-stage evaporators having



March 4, l1969 R. STARMER 3,431,179

MULTI-STAGE EVAPORATOHS HAVING DSTILLAND BY-PASS MEANS Filed Dec. l5,1966 JMW United States Patent O 3,431,179 MULTI-STAGE EVAPORATORS HAVINGDISTILLAND BY-PASS MEANS Roy Starmer, Durham, England, assigner toApplied Research and Engineering Limited, Durham, England, a Britishcompany Filed Dec. 15, 1966, Ser. No. 601,961 Claims priority,application Great Britain, Dec. 21, 1965,

54,045/65 Us. ci. 2oz- 173 Int. Cl. Bold 3/42, 3/02 5 Claims ABSTRACT OFTHE DISCLOSURE This invention relates to a multi-stage evaporators in adistillation plant employed, for example, in the production of distilledor potable water from sea-water or brine.

More speciiically this invention is related to the control of the ow ofliquid through the stages of the evaporator in order to control, forvarying throughputs, the liquid levels in the various stages, some suchcontrol means being beneficial since it is found that a high rate offlow tends to produce too high a level in at least some stages and thata slow rate of ow may allow the condition which is termed undersealingAccording to the invention a multi-stage evaporator comprises asuccession of stages, a submerged passage or aperture between each stageand the succeeding stage whereby a stream of liquid can ow through thesuccession of stages, and means for controlling the levels of the liquidin at least some of the stages, which means comprise a by-pass passageconnecting two successive stages, in addition to the aforesaid passageor aperture between the two stages, and means for controlling the rateof flow of liquid through the by-pass passage.

In one form of the invention the rate of ow through the by-pass passageis controlled by an adjustable valve.

In another form of the invention the rate of flow through the by-passpassage is controlled by interchangeable members within the by-pass,each member having a different size or orifice.

The evaporator is preferably a flash evaporator.

The or each opening provided by the passage or aperture between eachstage and the preceding stage of the evaporator yfor allowing the Huidto flow through the succession of stages of the evaporator, may be fixedor maybe adjustable.

An evaporator in accordance with the invention allows a faster rate ofilow at least between two of the evaporator stages than is possible witha similar evaporator which is not provided with the by-pass passage.Furthermore, the range of the rate of flow can be still furtherincreased by reducing the size of the passage or aperture between thestages having the by-pass passage whereby, with the by-pass passageclosed, the rate of ow would be slower than would otherwise be the case.

A by-pass passage may be provided between more than one set of twosuccessive stages.

By way of example, a specific embodiment of a multistage evaporator inaccordance with the invention will now be described with reference tothe accompanying ICC diagrammatic drawings in which:

FIGURE 1 is a layout of the evaporator; and

FIGURE 2 is a perspective view of the dividing wall between two stagesof the evaporator shown in FIGURE 1 to show means for adjusting the sizeof the orifice therein.

With reference to the drawings, the evaporator is a ash evaporator andcomprises ve stages 9A through 9E, each stage having a lower associatedportion 10A through 10E through which a stream of brine is fed and inwhich a part of the brine is flashed off, the steam evolved passing intotheir respective upper portions 11A through 11E in which portion thesteam condenses on a condensing surface 12 to form a distillate. Thepart of the brine which is not ilashed otl" passes into the succeedingstage through an associated orifice 13 or 13a in the wall 14 whichdivides the two stages.

It is normal that the sizes of the orifices 13, 13a determine the levelof the brine in the stages of the evaporator and it is desirable thatthe size of each orifice 13, 13a should be progressively greater thanthe preceding orifice (although, in practice, such increases arenormally carried out in steps, there 'being a number of stages betweeneach increase in the size of the orifice). A level controller, shown inFIGURE l as a ball-cock 15, is also provided in the last stage of theevaporator to assist in the control of the level of the brine.

Brine is fed into the evaporator at 17, the brine then passing through anumber of tubes, which comprise the aforesaid condensing surface 12 ofeach stage, to la heater 18 and then to the lower portion 10A of theiirst stage of the evaporator. A pump 19 is provided for returning thebrine that is not flashed off in any of the stages of the evaporatorinto the evaporator feed. The distillate is discharged at point 20.Also, the steam evolved in the last stage 9E of the evaporator iscondensed on a condensing surface 23 cooled by a fluid which isindependent of the evaporator feed.

'Ihe level of the brine in the stages of the evaporator has beendescribed above as being dependent on the sizes of the orifices 13, 13aand the level controller 15. The evaporator shown in FIGURE 1, however,also has a bypass passage 21 between the second and third stages, 9B,9C, respectively, which passage 21 is provided with means 22 forcontrolling the rate of flow therethrough. 'Ihe means 22, in thisexample is an adjustable valve but it could comprise a set of plates forinsertion into the passage, each plate having an orice therein of ladifferent size except yone plate which has no oriiice and comprises ablanking-ol plate.

In addition, the orifice 13a in the wall 14 dividing the second stage 9Band the third stage 9C is of a smaller size than would normally beemployed. Thereby, when the bypass valve 22 is shut-01T, the level ofthe brine in at least the preceding stage, is greater than wouldotherwise be the case. Similarly when the valve 22 is fully open, thelevel of the brine in at least the preceding stage 9B is less than foran evaporator that is not provided with the bypass passage 21 and thathas the orifice 13a between the second and third stages of normal size.The size of the orifice 13a may be iixed or, as shown in FIGURE 2, maybe adjustable by means of vertical adjustment of a plate 24 within theguideways 25` The vertical position of this plate 24 may be adjusted bymeans of a vertical rack 30 opstanding from the plate, and a pinion 31in mesh with the rack, the pinion being mounted on a shaft 32 whichpasses through a bearing 33 xcd to the respective wall 14, and projectsout of the lower portion 10. A wheel 34 is fitted to the free end of theshaft 32 to cause rotation of the pinion 31 and hence vertical movementof the rack 30 and the plate 34.

The levels of the brine in the various stages 9A through 9E, as shown inFIGURE 1, are appropriate for an evaporator in which the valve 22 is ina substantially shut-oli position, i.e., the rate of flow between thesecond stage 9B and the third stage 9C is reduced. It is estimated thatif the size of the orifice 13a in the dividing wall 14 between thesecond and third stages is, or is adjusted so that it is, 15% smallerthan would normally be the case and if the by-pass passage 21 is capableof passing 30% of the flow between these stages 9B, 9C, then operationof the control means 22 enables a depth control corresponding to a owcontrol of 15% above and below the range of depth control of anevaporator that is not provided with the by-pass passage 21 and that isnot provided with the smaller orifice 13a.

The invention is not restricted to the specic details of the evaporatordescribed above. For example, the sizes of some or each of the orifices13 may be adjustable. Also, in the case of an evaporator lhaving tivestages 9A through 9E, as shown in FIGURE l, a by-pass passage betweenthe second stage 9B and the third stage 9C in addition to the levelcontroller (with or without the orifices being adjustable), is suicientto provide the necessary control to the depth of the brine in the iivestages. However, when more stages are added it may be necessary toprovide one or more additional by-pass passages between other pairs ofstages.

I claim:

1. A multi-stage evaporator comprising a shell, a plurality of spaced,upright partitions within said shell thereby forming a succession ofevaporator stages, each of said partitions at their bottom ends havingan aperture extending across the full length thereof to permit a streamof liquid to ilow from each said stage to its succeeding stage, at leastone open-ended by-pass conduit attached to the bottom of said shelldirectly beneath at least one of said partitions with an end of saidconduit positioned on either side thereof for connecting at least one ofsaid stages to a succeeding stage and, means in said at least oneconduit for controlling the tlow rate of tiuid therethrough, whereby adierence in levels of liquid between the stages connected by saidconduit can be controlled.

2. An evaporator according to claim 1, wherein said control meanscomprises an adjustable valve.

3. An evaporator according to claim 1, wherein said control meanscomprises a plate having an orifice therein of a size depending on thespecific rate of ow desired through said conduit.

4. An evaporator according to claim 1, further including means foradjusting the size of one of said partitioned apertures.

5. An evaporator according to claim 1, wherein two open-ended by-passconduits attached to the bottom of said shell are provided.

References Cited wrLBUR L. BAsCoMB, 1R., Primary Examiner.

U.S. Cl. X.R.

